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WATER pUAl1TY <br />• The summary of the water quality data for the spring is presented in Tables 34 and 35. A plot of dissolved <br />• <br />solids for the #1 Strip Pit is presented in Figure 29. It indicates that the dissolved solids level of the <br />discharge has increased from an average of approximately 900 mg/t in 1982 and 1983 to almost 1,400 <br />mg/1 in 1986, and then decreased to less than 1,200 mg/1 since 1987. At the end of 1990 the Iron <br />concentration increased dramatically. The apparent increase in iron was found to be due to a sampling <br />error caused by frozen conditions. Samples collected in 1991 showed much lower iron concentrations. The <br />increase in TDS and field conductivity appearing in about June, 1991 may be related to the higher TDS in <br />the re-issue of the 7 North Angle discharge in May of 1991. The TDS in the 7 North Angle discharge <br />averaged about 1280 mg/1 in 1991 which slightly exceeds the TDS measured in the # 1 Strip Pit discharge <br />during July and October, 1991. <br />PONDS <br />Sediment ponds did not discharge during 1991. Consequently Table 36, listing water quality monitoring <br />results for the year, is not included. <br />HYDROLOGIC IMPACTS <br /> <br />No significant unpredicted adverse impacts were detected 1991. The continued drawdown in the Middle <br />Sandstone unit is determined to be the most significant impact related to mining operations associated with <br />Mines 5 and 6. The Probable Hydrologic Consequences section of the Permit predicted drawdown in the <br />Middle Sandstone unit associated with mining the F and E coal seams at Mines 5 and 6, although the extent <br />and magnitude of the drawdown were not quantified. A worst case evaluation was, however, prepared for <br />the overlying 7wentymile Sandstone. <br />10 <br />